PURPOSE: To surely carry out an adjustment for a focal point for an image to be picked in a dark-field by a simple voice from a user so as to enhance the manipulatability during working in the dark.

CONSTITUTION: A voice signal Sb is transmitted to a vocal code vibration processing part 21 from a voice code vibration detecting part 20 attached to the throat M, and the voice is identified. If a voice 'A' is identified, a drive signal generating part 22 delivers a drive signal Sa for adjusting the focus points of motor driven objective lenses 12a, 12b to a far distance. If a voice 'O' is identified, the drive signal generating part 22 delivers a drive signal Sa for adjusting the focus points of the lenses 12a, 12b to a near distance. Further the voice 'A' and 'O' are successively issued, the adjustment for the focus points to a far or near distance is automatically and successively carried out.